L-amino acids are useful in many industrial fields such as pharmaceuticals, agricultural chemicals and foods. With regard to the industrially useful L-amino acid for example, there have been known L-lysine, L-threonine, L-isoleucine and L-proline used as additives for animal feeds, ingredients for health foods, amino acid transfusion, etc.; L-arginine and L-ornithine used as ingredients for hepatic function promoters, amino acid transfusion and multi-amino acid preparations; L-histidine used as hepatic function promoters and precursor for histamine; L-phenylalanine used as a precursor for sweeteners; and L-tert-leucine used as an intermediate for various pharmaceuticals. Accordingly, there has been a demand for an efficient production of those useful L-amino acids in a state of being separated from D-amino acids.
As to a process for producing the L-amino acid, there has been a conventional method where a racemic N-acylamino acid is synthesized and then only an L-form compound in the racemic modification is hydrolyzed using an enzyme called an L-aminoacylase. In result, only L-amino acid is specifically produced. As to the L-aminoacylase used for that method, there have been known, for example, an L-aminoacylase derived from Penicillium funiculosum (Patent Document 1) and an L-aminoacylase derived from Streptomyces mobaraensis (Patent Document 2).
However, those L-aminoacylases are excellent in a hydrolyzing ability, their substrate specificity is still unsatisfactory whereby they are unable to recognize an N-acyl-L-tert-leucine as a substrate. Therefore, according to the method using conventional L-aminoacylase, an N-acyl-DL-tert-leucine is unable to be optically resolved and it has been impossible to produce L-tert-leucine which is a useful intermediate for pharmaceuticals.